When a skin invasive action is to be performed it is important that the site which is chosen for the action is a suitable one. This is particularly important if the skin invasive action is of a kind which needs to be repeated. Examples of such actions are repetitive injections of drugs, e.g. insulin for people with diabetes, repetitive collection of blood samples, tissue samples, such as samples from subcutaneous layers, or samples of other kinds of body fluids. This may, e.g., include blood glucose measurements for people with diabetes. When a particular area of the skin has been subject to a skin invasive action, that area will, for some time, be unsuitable for another skin invasive action of the same kind.
Thus, multiple skin invasive actions into the same spot within a relatively short period of time may cause alterations to the fat, also known as ‘lipodystrophy’. This can lead to a thickening of the fat at the site of the skin invasive action and can cause lumps or slumps in the skin. In case the skin invasive action is the injection of a drug, a thickening of the fat at the site may alter the drug absorption at the site, thereby causing an unknown and uncontrollable dose of the drug to be absorbed. Furthermore, in case the person in question sometimes injects the drug in a site which is damaged and sometimes in a site which is not damaged, the absorbed amount of drug will vary from one injection to the other, thereby causing undesirable fluctuations in the absorbed amount of drug. For instance injecting insulin into the same spot too frequently can cause lipodystrophy, and thereby potentially alter the insulin absorption as described above. This may be dangerous and potentially lethal. In case the skin invasive action is collection of blood samples or tissue samples it is also undesirable to perform the action in a site which has recently been used for another skin invasive action of the same kind because the skin or one or more of the subcutaneous layers will suffer damage, at least temporarily, when a sample is collected, and scar tissue may be formed making it more difficult to penetrate the skin.
It is therefore desirable to organize repetitive skin invasive actions in such a way that the sites used for the actions is circulated in such a way that use of a site which has previously been used within a relatively short period of time is avoided. To this end mechanical systems have previously been developed for guiding a person in choosing a site for a repetitive skin invasive action. Such a system is disclosed in GB 2 202 445 which discloses a double sided flexible injection guide grid having a number of apertures each clearly identified or defined which aids a person requiring frequent subcutaneous injections to vary the site of the injection and thus avoid complications which sometimes occur when frequent injections are given into the same small area of skin. The injection guide grid is positioned at the injection site (e.g. the stomach area of a person) and an injection is given in an area corresponding to one of the apertures. The person has to fill in a separate record card in order to keep track of which apertures have been used for injections recently, thereby avoiding that an injection is performed into a site which has recently been used for an injection. However, the injection guide grid disclosed in GB 2 202 445 is rather cumbersome to use because the person has to keep track of the injection sites in a separate record card, and there is therefore a risk that the person forgets or does not bother to fill in the record card after an injection has been performed. Furthermore, the fact that the record card has to be filled in by a person introduces the risk of human errors, i.e. the risk that the person simply fills in the record card in an erroneous manner, thereby introducing the risk that the same site is used for the next injection. Furthermore, the injection guide grid is a very inaccurate way of keeping track of the injections, and it is only possible to keep track of one body part at a time.
WO 93/02720 discloses an automatic programmable injection/aspiration device for administration of medicaments. The device comprises means for controlling the rate, direction and extent of needle insertion, fluid injection and needle withdrawal. The device is adapted to interrogate the injection site in order to ensure that the injection is performed at a desired site, i.e. in a correct kind of tissue, in order to avoid that pharmaceutical substances or other fluids are not unintentionally injected into a blood vessel, a lymph vessel or into cerebrospinal fluid. To this end an attempted aspiration is made in order to interrogate the injection site (i.e., essentially, as understood in the art the volume of tissue immediately adjacent to and in fluid communication with the open end of the needle) for the presence of blood, lymph, cerebrospinal fluid, or the like. Thus, the interrogation is performed in an invasive manner, i.e. it is performed after the device has penetrated the skin of the person, and it is therefore not possible to avoid the problems related to choosing an appropriate area part of the skin mentioned above.
U.S. Pat. No. 5,865,744 discloses a method and a system for internally delivering a therapeutic agent to a patient under the automatic control of a computer. A scanning system generates one or more images of the patient's anatomy showing an anatomical region into which it is desired to deliver the agent. Based on the image(s) a desired site, typically a tumour, for an invasive action is located, and the injection needle is moved to inject the drug exactly at the desired site.
U.S. Pat. No. 6,156,008 discloses an injection site locating device including a sensor to detect and give an indication of a suitable injection site to minimise creation of subdermal hematomas from injection of the liquid medication by the injector. In particular, the sensor detects the presence of high and/or low blood flows and indicates that a suitable injection site is over the low blood flow.
The devices disclosed in U.S. Pat. No. 5,865,744 and U.S. Pat. No. 6,156,008 are not concerned with assisting a person in choosing a site for a skin invasive action in such a manner that the problems arising from repetitive skin invasive actions described above are avoided.